Rift Mob:Tormented Wisp

This rare spawns as 4-5 level 15 wisp mobs with 833 HP each. Found among the spiders in Lakeside Outpost in Freemarch. Only killing one is needed for achievement credit, and a despawn timer starts for the remaining mobs once one is killed. However, each can drop the rare's loot, so the more you kill before they despawn, the better the looting can be.